I'm going to play devil's advocate here. Forte is going to be 27 years old this season and has "above average" mileage on his body. What type of contract is effective in this scenario? Logic and history dictate that he has only two good seasons left.
Would he even accept a 3 or 4 year deal? 3 being best for the Bears, 4+ better for Forte. IMO - there is no way Chris Johnson and AP live out the deals they just signed.
The devil behind the scene is: locker room moral, Fortes' overall happiness, team reputation, competetiveness, and cap health. A lot can swing during this negotiation.